After a plate-shaped sample, such as a semiconductor wafer, e.g. a silicon wafer, used for manufacturing semiconductor integrated circuits or a glass substrate used for manufacturing liquid crystal devices, is held on a support stage of a manufacturing apparatus or an inspection apparatus in a manufacturing process, for example, a processing treatment or an inspection is performed on the sample. In the manufacturing process, since a plurality of manufacturing apparatuses and inspection apparatuses are generally used, as a device configured to hold a sample, such as silicon wafer, on a support stage, various types of devices have been proposed in accordance with the types of manufacturing apparatuses and inspection apparatuses used in a manufacturing process and the types of transport apparatuses transporting a sample to the following apparatus.
For example, in the case of a semiconductor integrated circuit, in recent years, the semiconductor integrated circuit has been increasingly required to be more finely designed and to have a higher density. In concomitance with this requirement, a sample holder is further required to improve the thermal uniformity of a surface thereof which holds a sample. In addition, in recent years, in order to perform wiring pattern processing having a high aspect ratio on a semiconductor wafer, it has been required to apply a high frequency wave to a sample holder. In concomitance with this requirement, the sample holder is required to improve the withstand voltage.
Japanese Unexamined Patent Application Publication No. 3-108737 (hereinafter referred to as “Patent Document 1” in some cases) has disclosed an electrostatic chuck formed of a plurality of ceramic layers, and in this electrostatic chuck, a flow path which allows a cooling medium to flow therethrough is formed in an intermediate ceramic layer. When the balance between heating and cooling is controlled at each portion by this structure, the thermal uniformity of the surface of the electrostatic chuck can be improved.
However, in the electrostatic chuck disclosed in Patent Document 1, it has been difficult to further improve the thermal uniformity while the strength in the vicinity of the surface which holds a sample is maintained. In particular, as a method to improve the thermal uniformity of the surface which holds a sample, an improvement in thermal conductivity of the ceramic layer has been conceived. However, in order to improve the thermal conductivity of the ceramic layer, when the average grain diameter of ceramic grains thereof is increased, since the gap between grain boundaries is increased, the strength of the ceramic layer may be decreased in some cases. As a result, the strength in the vicinity of the surface which holds a sample may be degraded in some cases. Accordingly, for example, by a pressure to be applied during assembly and/or a thermal stress generated under heat cycle conditions, the ceramic layer may be damaged in some cases. In addition, when a high frequency wave is applied to the electrostatic chuck, if the average grain diameter of the ceramic grains is large, the gap between grain boundaries is increased, so that electricity is liable to pass through the grain boundaries. As a result, breakdown of the ceramic layer may occur in some cases.
On the other hand, in order to increase the strength in the vicinity of the surface which holds a sample, when the average grain diameter of the ceramic grains of the ceramic layer is decreased, the number of interfaces between the grains is increased, so that the thermal conductivity may be degraded in some cases. As a result, the thermal uniformity of the surface which holds a sample may be degraded in some cases.